Wireless communication systems are well known and consist of many types, including land mobile radio, cellular radiotelephone, and personal communication systems. With each communication system, data is transmitted between a transmitting communication device and a receiving communication device via a communication resource that includes a communication channel that operates over a physical resource, typically a frequency bandwidth. Bandwidth is limited and equipment is expensive, and therefore many schemes have been developed for multiplexing many different users over the same frequency bandwidth.
One such communication system currently being developed is the next generation Code Division Multiple Access (CDMA) cellular communication system, commonly referred to as Wideband Code Division Multiple Access (WCDMA). In a WCDMA communication system, all mobile station and base station transmissions occur simultaneously within the same frequency band. Therefore, a received signal at a base station or a mobile station comprises a multiplicity of frequency and time overlapping coded signals from mobile stations or base stations, respectively. Each of the coded signals included in the received signal is transmitted simultaneously at the same radio frequency and is distinguishable only by the coded signal's specific orthogonal code (i.e., a communication channel).
A typical WCDMA communication system 100 of the prior art is shown in FIG. 1. Under current WCDMA Random Access Channel (RACH) standards, that is, European Telecommunications Standards Institute Technical Specifications (ETSI TS) 3GPP specifications TS25.215 and TS25.321, a mobile station (MS) 102 requests a first communication channel, that is, a reverse link traffic channel, 104 by transmitting a series of preambles via a second communication channel, that is, a reverse link control channel, 106 to a wireless infrastructure that includes a base station 108. MS 102 adjusts the power level of each preamble of the series of preambles so that each preamble is transmitted at a different power level than the other preambles in the series of preambles. In turn, base station 108 grants MS 102 access to communication channel 104 by acknowledging a preamble that is received at an appropriate power level. Upon receiving an acknowledgment (‘ACK’) of a preamble from base station 108, MS 102 transmits a message to the base station in communication channel 104. In turn, so long as MS 102 fails to receive an acknowledgment of a preamble, MS 102 continues to transmit preambles to base station 108.
By MS 102 varying the power levels of the preambles, and base station 108 acknowledging only an appropriately power-adjusted preamble, MS 102 and base station 108 are able to determine an appropriate power level for their communications. Thus the preambles serve both a power control function and an access request function. However, base station 108 will not acknowledge a preamble so long as a demodulator 110 in the base station is engaged in demodulation of a signal received via communication channel 104. Instead, when base station 108 receives an appropriately power-adjusted access request and no communication channel is available, the base station transmits a NAK to MS 102. In response to receiving the NAK, MS 302 backs off for a random period of time and then repeats the process of transmitting a series of successively incremented communication resource access requests.
For example, FIG. 2 is a timing diagram 200 of an exemplary process of allocating a communication resource of the prior art. FIG. 2 includes multiple time lines 214–216 that respectively correspond to MS 102, base station 108, and demodulator 110 and that are each subdivided into multiple time units 218. Each time unit has a time duration of 1.33 milliseconds (ms), which is a typical length of an access slot, or preamble transmission, in a CDMA communication system.
As depicted in FIG. 2, MS 102 transmits a first preamble 202 at a time when demodulator 110 is demodulating a first message 212. If preamble 202 is at an appropriate power level but demodulator 110 is engaged when base station 108 receives the preamble, the base station does not acknowledge the preamble (assuming that preamble 202 is at an appropriate power level) and instead transmits a NAK 203 to MS 102. In response to receiving the NAK, MS 102 backs off for a random period of time and then repeats the process of transmitting a series of successively incremented preambles 204, 206, 208. By the time base station 108 receives a second appropriately power-adjusted level preamble 208, demodulator 110 has finished demodulating message 212. Since demodulator 110 is now available to demodulate a new message, base station 108 transmits an ACK 210 back to MS 102. Upon receiving ACK 210, MS 102 transmits message 214 to base station 108, which conveys the message to demodulator 110 for demodulation.
Since base station 108 does not acknowledge an appropriately power-adjusted preamble until demodulator 110 is available to demodulate a new message, the demodulator may be idle for a period of time 220 corresponding to awaiting receipt by the base station of a new, appropriately power-adjusted preamble 208, acknowledgment by the base station of the new preamble, transmission of a message by the MS in response to receiving the acknowledgment, and receipt of the message by the base station. Such idle time is wasted time that reduces a throughput of communication channel 104 and a user capacity of system 100. Furthermore, the repeated preamble transmissions consume a capacity of control channel 106.
Therefore, a need exists for a method and an apparatus for communication resource allocation that reduces the idle time of a demodulator and that increases the throughput of a communication channel and the capacity of a broadband communication system.